Method for making fiber optic assembly with crimped end connector

ABSTRACT

In a preferred form, this disclosure relates to a fiber optic assembly comprising a fiber optic bundle having an outer flexible sheath of a given external diameter and an end connector crimped onto an end portion of the bundle. The end connector is in the form of a metal sleeve and has a section intermediate its ends which is crimped onto the fiber optic bundle. The section is substantially hexagonal in shape, as viewed in cross section, and has substantially flat sides and apices at the intersection of the sides and with the flats lying on an inscribed circle having a diameter which is less than the external diameter of the sheath whereby the sheath is deformed upon the section being crimped thereon so as to have a radial thickness adjacent the flat sides which is less than the radial thickness of the sheath fore and aft of the crimped section.

350-4520. SR 04-11-72 OR United States Patent Seagreaves [72] Inventor:

[73] Assignee:

George F. Seagreaves, Warren, Ohio General Motors Corporation, Detroit,Mich.

[22] Filed: Nov. 18, 1970 [21] Appl.No.: 90,722

[56] References Cited UNITED STATES PATENTS 2,587,095 2/1952 Bergan..287/75 2,622,314 12/1952 Bergan ..29/5l7 [451 Apr. 11, 1972 3,423,581l/l969 Baer ..350/96BX Primary Examiner-David H. Rubin Attomey-W. E.Finken and W. A. Schuetz [5 7] ABSTRACT In a preferred form, thisdisclosure relates to a fiber optic assembly comprising a fiber opticbundle having an outer fiexi ble sheath of a given external diameter andan end connector crimped onto an end portion of the bundle. The endconnector is in the form of a metal sleeve and has a sectionintermediate its ends which is crimped onto the fiber optic bundle. Thesection is substantially hexagonal in shape, as viewed in cross section,and has substantially flat sides and apices at the intersection of thesides and with the flats lying on an inscribed circle having a diameterwhich is less than the external diameter of the sheath whereby thesheath is deformed upon the section being crimped thereon so as to havea radial thickness adjacent the flat sides which is less than the radialthickness of the sheath fore and aft of the crimped section.

2 Claims, 7 Drawing Figures PATENTEDAPR 11 I972 3,655,275

ATTORNEY METHOD FOR MAKING FIBER OPTIC ASSEMBLY WITH CRIMPED ENDCONNECTOR The present invention relates to a fiber optic assemblycomprising a fiber optic bundle having an outer flexible sheath and anend connector having a hexagonal shaped section which is crimped onto anend portion of the bundle, and to a method of making the same Fiberoptic assemblies are used to transmit light from a light source to alocation remote from the light source. For example, in automotivevehicle applications they are used as an indicating means, such as toindicate when a light bulb is burned out, and as a means forilluminating dials, switches, etc.

Fiber optic assemblies usually comprise a fiber optic bundle, plasticlenses or socket bodies positioned adjacent the light source and theremote location to which the light'is to be transmitted and endconnectors attached to the opposite ends of the fiber optic bundles forconnecting the same to the lenses or socket bodies. The fiber opticbundle includes a plurality of plastic or glass fibers or cores, each ofwhich is coated with a substance having a lower light refraction indexthan the fiber or core, and an opaque flexible, deformable outer sheathor jacket, usually made of plastic, such as polyvinyl chloride,surrounding the fibers or cores for protecting the same.

Providing suitable end connectors for fiber optic bundles which meetrequired design criteria has presented some difficulty. These criteriaare (I) the end connector, when crimped onto the fiber optic bundle,must be able to withstand normal axial thrust loads during assembly,disassembly and normal use without coming off of the plastic sheath and(2) the radial pressure exerted on the bundle by the connector must bekept at a minimum because excess radial pressure exerted against thefiber cores affects the light transmitting capability of the fiber opticbundle.

Also, to maximize the light transmitting capabilities of the fiber opticbundle, the ends thereof are polished. To polish the same it isnecessary to coat the same with an epoxy resin to bond the individualfibers together after the end connector is crimped thereon. The crimphas to be of a sufficient tightness to prevent the flow of epoxytherepast due to capillary action.

An object of the present invention is to provide a new and improvedfiber optic assembly comprising a fiber optic bundle having an outerflexible sheath of a given external diameter and radial thickness and anend connectorin the form of a sleeve having an intermediate sectioncrimped onto the bundle, and in which the crimped intermediate sectionis substantially polygonal in shape, as viewed in cross section, and hasits flat sides lying on an inscribed circle having a diameter which isless than the given diameter of the sheath so that when the section iscrimped thereon the radial thickness of the sheath adjacent the flatsides is less than the given radial thickness of the sheath fore and aftof the crimped section whereby the end connector is securely held on thebundle and exerts only a minimal radial pressure on the fibers or cores.

A further object of the present invention is to provide a new andimproved fiber optic assembly comprising a fiber optic bundle having anouter deformable sheath of a given external diameter and radialthickness and an end connector in the form of a seamless sleeve havingan intermediate section which is crimped onto the bundle, and in whichthe intermediate section is hexagonal in shape, as viewed in crosssection, and has its flat sides lying on an inscribed circle having adiameter which is less than the given diameter of the sheath so thatwhen the intermediate section is crimped onto the bundle the radialthickness of the sheath adjacent the flats is less than the given radialthickness of the sheath fore and aft of the crimped section whereby theend connector is securely held on the bundle and exerts only minimalradial pressure against the fibers.

Yet another object of the present invention is to provide a new andimproved fiber optic assembly, as defined in the next preceding object,and wherein the end connector includes a second hexagonal section whoseflats lie on an inscribed circle having a diameter slightly less thanthe diameter of the flexible sheath so that the second section providessurface tension between it and the sheath to aid in securely holding theend connector on the bundle.

Another object of the present invention is to provide a new and improvedmethod of making a fiber optic assembly wherein an annular metal ferruleor end connector istightly crimped intermediate its ends to a fiberoptic bundle to provide a polygonally, preferably hexagonally, crimpedsection to securely attach the connector to the bundle and to preventany flow via capillary action of a bonding resin past the crimpedsection when the end of the fiber optic bundle is subsequently coatedwith the resin and polished.

The present invention further resides in various novel constructions andarrangement of parts, and further objects, novel characteristics andadvantages of the present invention will be apparent to those skilled inthe art to which it relates and from the following detailed descriptionof the illustrated embodiments thereof made with reference to theaccompanying drawings forming a part of this specification and in whichsimilar reference numerals or characters are employed to designatecorresponding parts throughout the several views, and in which:

FIG. 1 is an elevational view of the preferred embodiment of the fiberoptic assembly of the present invention;

FIG. 2 is an axial cross-sectional view taken approximately along line2-2 of FIG. 1;

FIG. 3 is a cross-sectional view taken approximately along line 3-3 ofFIG. 2;

FIG. 4 is a plan view of a second embodiment of the fiber optic assemblyof the present invention;

FIG. 5 is a side elevational view with parts shown in section of theassembly shown in FIG. 4;

FIG. 6 is a cross-sectional view taken approximately along line 6-6 ofFIG. 5; and

FIG. 7 is a cross-sectional view taken approximately along line 7-7 ofFIG. 4. I

As representing a preferred embodiment of the present invention, FIG. 1of the drawings shows a fiber optic assembly 10. The fiber opticassembly 10 comprises, in general, a fiber optic bundle l2 and an endconnector 14 which is crimped onto an end portion ofthe fiber opticbundle. The end connector 14 is adapted to be suitably secured to alense or socket body (not shown) adjacent a light source or a remotelocation to which the light is to be transmitted.

The fiber optic bundle 12 can be of any suitable or conventionalconstruction and preferably comprises a plurality of light transmittingglass fibers or cores 18 which are individually surrounded by asubstance having a lower light refraction index than the fibers or cores18. Surrounding or encasing the plurality of fibers or cores throughouttheir length is a flexible outer sheath or jacket 20, preferably madefrom a plastic material such as polyvinyl chloride. The flexible outersheath 20 has a given nominal external diameter a and a given radialthickness.

The end connector 14 for connecting the fiber optic bundle 12 to anassociated lense or socket body (not shown) comprises a one piece, thin,seamless, metal sleeve or ferrule. The end connector is generallycylindrical and has an internal diameter b which is slightly larger thanthe nominal external diameter a of the fiber optic bundle 12. The endconnector 14 receives an end portion of the fiber optic bundle 12 andincludes a section 25 intermediate its ends which is crimped onto thefiber optic bundle 12.

The crimped section 25 is polygonal, preferably hexagonal, in shape, asviewed in cross section. The section 25 is crimped from a circular ringconfiguration to its hexagonal ring shaped configuration by a suitablepunch and die apparatus or crimping tool. The hexagonal shaped section25 has substantially fiat sides 25a and apices 251 at the intersectionof the flat sides. The flat sides on their inner surface lie on aninscribed circle 30 having a diameter whichis less than the givenexternal diameter of the jacket or sheath. The apices of the hexagonalsection 25 at their inner corners lie on a circumscribed circle 32having a diameter which is no greater than, but

preferably less than, the external given diameter of the sheath. Whenthe hexagonal section 25 is crimped onto the sheath, the sheath adjacentthe crimped area is deformed and displaced so as to have a radialthickness adjacent the flats and apices which is less than the givenradial thickness fore and aft of the section 25, as shown in FIG. 2.This difference in the thickness of the sheath provides sufficientresistance to axial movement of the end connector 14 relative to thebundle 12 when subjected to axial thrust loads and thus, securelyretains the end connector 14 on the bundle 12. Also the hexagonal ringshaped crimp section 25, although exerting some radial pressure, doesnot exert pressure of a magnitude such that the light transmittingcapabilities of the fiber optic bundle are impaired. The end connectorat one end has a radially extending flange 35 which is adapted to bereceived within the groove of a suitable lense body (not shown) tosecurely retain the fiber optic bundle 12 to the lense.

The hexagonal ring crimp section also has another advantage. In themaking of the fiber optic assembly 10, the end connector 14 is as shownin FIG. I. Then crimped onto the bundle 12 adjacent an end portionthereof, the end of the bundle is coated with an epoxy resin to bond theindividual fibers together to enable the end thereof to be thereafterpolished.

This epoxy resin via capilary action travels along the fiberopticbundle. The hexagonal ring crimp section 25 will prevent any travel ofepoxy resin therepast.

FIGS. 4 through 7 show an alternate fiber optic assembly 40 constructedin accordance with the present invention. Corresponding parts of thefiber optic assembly 40 shown in FIGS. 4 through 6 will be given thesame reference numerals, but with a prime affixed thereto. The fiberoptic assembly shown in FIGS. 4-6 also includes a second section 50adjacent its forward end which is crimped so as to have a hexagonalshape, as viewed in cross section. This latter section 50, however, isnot crimped as much as the section 25, but is crimped to the extent thatthe flats 50a thereof on their inner surface lie on an inscribed circle52 having a diameter which is slightly less than the external diameterof thesheath 20' so that the sheath 20 will be very slightly deformedand in frictional engagement with the section 50 so as to aid inpreventing axial movement of the connector 40 relative to the bundle 12when subjected to axial thrust loads.

To further increase the resistance to pull off when subjected to axialthrust loads, the second section can also be provided at diametralopposite locations with a pair of inwardly directed darts 55 formed by asuitable tool depressing radially inwardly from the sides. These dartswould cut into the sheath 20' of the fiber optic bundle, but not throughthe same.

Although the illustrated embodiment thereof has been described in greatdetail, it should be apparent that certain modifications, changes, andadaptations may be made in the illustrated embodiment, and that it isintended to cover all such modifications, changes and adaptations whichcome within the spirit of the present invention.

What is claimed is:

1. In a method for making a fiber optic assembly which includes thesteps of attaching an annular metal end connector adjacent one end of afiber optic bundle having a plurality of glass cores surrounded by anannular flexible sheath of a given nominal external diameter, coating anend of the fiber optic bundle with a bonding resin to bind the corestogether adjacent said end, and polishing the coated end of the fiberoptic bundle, the improvement being that said end connector is attachedto said bundle by crimping an annular section spaced inwardly from saidone end to provide a polygonally shaped section having flat sides andapices at the intersection of the sides and with the sides lying on aninscribed circle having a diameter which is substantially less than thenominal external diameter of the sheath and with the apices at theirradially innermost ends lying on an inscribed circle having a diameterno greater than the nominal external diameter of the sheath whereby thesheath has a radial thickness at the sides of the section which issubstantially less than its radial thickness fore and aft of the crimpedsection and whereby said bonding resin is prevented from flowing viacapillary action along the fiber optic bundle past the crimped section.

2. In a method for making a fiber optic assembly which includes thesteps of attaching an annular, seamless, metal end connector adjacentone end of the fiber optic bundle having a plurality of glass coressurrounded by an annular flexible sheath of a given nominal externaldiameter, coating an end of the fiber optic bundle with a bonding resinto bind the cores together adjacent said end, and polishing the coatedend of the fiber optic bundle, the improvement being that said endconnector is attached to said bundle by crimping an annular sectionspaced inwardly from said one end to provide a hexagonally shapedsection, as viewed in cross section, having flat sides and apices at theintersection of the sides and with the sides lying on an inscribedcircle having a diameter which is substantially less than the nominalexternal diameter of the sheath and with the apices at their radiallyinnermost ends lying on an inscribed circle having a diameter which isless than the nominal external diameter of the sheath whereby the sheathhas a radial thickness at the sides of the hexagonally shaped sectionwhich is substantially less than the radial thickness fore and aft ofthe crimped section to securely retain the connector on the sheath andwhereby said bonding resin is prevented from flowing via capillaryaction along the bundle past the hexagonally crimped section.

2 3 UNITED STATES PATENT OFFICE CERTIFICATE OT CORRECTTON Patent No. 3,655 275 Dated April 11, 1972 lnventortls) George F. Seagreaves It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

column 3, lines 18 through 26 should read The hexagonal ring crimpsection 25 also has another advantage. In the making of the fiber opticassembly 10, the end connector 14 is first crimped onto the bundle 12adjacent an end portion thereof, as shown in Figure l. Then the end ofthe bundle is coated with an epoxy resin to bond the individual fiberstogether to enable the end thereof to be thereafter polished. This epoxyresin via capillary action travels along the fiber optic bundle. Thehexagonal ring crimp section 25 will prevent any travel of epoxy resintherepast.-

Signed and sealed this 3rd day of October 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSGHALK Commissioner of PatentsAttesting Officer

1. In a method for making a fiber optic assembly which includes thesteps of attaching an annular metal end connector adjacent one end of afiber optic bundle having a plurality of glass cores surrounded by anannular flexible sheath of a given nominal external diameter, coating anend of the fiber optic bundle with a bonding resin to bind the corestogether adjacent said end, and polishing the coated end of the fiberoptic bundle, the improvement being that said end connector is attachedto said bundle by crimping an annular section spaced inwardly from saidone end to provide a polygonally shaped section having flat sides andapices at the intersection of the sides and with the sides lying on aninscribed circle having a diameter which is substantially less than thenominal external diameter of the sheath and with the apices at theirradially innermost ends lying on an inscribed circle having a diameterno greater than the nominal external diameter of the sheath whereby thesheath has a radial thickness at the sides of the section which issubstantially less than its radial thickness fore and aft of the crimpedsection and whereby said bonding resin is prevented from flowing viacapillary action along the fiber optic bundle past the crimped section.2. In a method for making a fiber optic assembly which includes thesteps of attaching an annular, seamless, metal end connector adjacentone end of the fiber optic bundle having a plurality of glass coressurrounded by an annular flexible sheath of a given nominal externaldiameter, coating an end of the fiber optic bundle with a bonding resinto bind the cores together adjacent said end, and polishing the coatedend of the fiber optic bundle, the improvement being that said endconnector is attached to said bundle by crimping an annular sectionspaced inwardly from said one end to provide a hexagonally shapedsection, as viewed in cross section, having flat sides and apices at theintersection of the sides and with the sides lying on an inscribedcircle having a diameter which is substantially less than the nominalexternal diameter of the sheath and with the apices at their radiallyinnermost ends lying on an inscribed circle having a diameter which isless than the nominal external diameter of the sheath whereby the sheathhas a radial thickness at the sides of the hexagonally shaped sectionwhich is substantially less than the radial thickness fore and aft ofthe crimped section to securely retain the connector on the sheath andwhereby said bonding resin is prevented from flowing via capillaryaction along the bundle past the hexagonally crimped section.